An 18-year study of bees finally sheds light on something that may be wiping them out

For years, there's been suspicion that a class of pesticides
known as neonicotinoids are bad for bees. The chemicals, which
farmers apply to their crops to keep away insects that munch
through their harvests, are among the
most used bug-killers out there.

But ecologists have worried the chemicals also affect the insects
that help support harvests.

Bees have been mysteriously disappearing in what's called colony
collapse disorder, which some scientists believe neonicotinoids
are contributing to.

That's a problem because the pollination work bees do is
hugely valuable. Commercially managed honeybees produce about
$15 billion in value for the US alone and wild American bees
another $9 billion.

There's finally a study that tries to actually parse out the
effects neonicotinoids have on bees in the wild. It looks at 62
different wild bee species in the UK.

That's important because while only three species of
bees and bumblebees are kept by beekeepers and used commercially,
experts believe there are closer to 250 wild species in
the UK and
4,000 in the US. And while we don't manage them, we do
benefit from their pollination.

The new study, which was published August 16 in the
journal Nature
Communications, also looks at an 18-year timespan that begins
before neonicotinoids
were introduced in 2002. That means the researchers could
actually establish a baseline for how bees were doing before
farmers began widely using the chemicals.

Neonicotinoids are used particularly on rapeseed, one
variety of which is turned into canola oil. During the month or
two they bloom, the flowers turn swaths of the British
countryside a shocking yellow.

Some bees like the flowers; some don't. So the scientists were
able to divvy bees up by their taste for rapeseed, then look at
how their populations changed over almost two decades of surveys.

For a few bees, the scientists estimate
about a fifth of their population declines was due to
neonicotinoids.

That's not enough to kill off bees taken by itself. But
pesticides aren't the only challenge bees are facing. Climate
change, differences in how we use the land and what plants they
can feed on, and parasites and diseases that infect bees are also
putting a dent in populations.

And it doesn't necessarily mean we should stop using
neonicotinoids cold turkey. "It needs to be taken in a very
holistic perspective, you can't just say as long as we can save
the bees everything else can go to hell, that's not where you
want to be at," lead scientist Ben Woodcock told the
BBC.

The study isn't quite the
gold standard of science, since the researchers were just
watching what happened from changes already in place rather than
carefully controlling circumstances so that pesticide exposure
was the only difference between groups.

But that kind of study is really hard to do in ecology — and
getting a long-term, large-scale look at a range of species is
better information than we've had before.